Multi-level stacked mold system

ABSTRACT

An injection mold for use with a molding press has four mold levels in axially stacked relation, permitting a substantial doubling of output for a given size of press as compared with a back-to-back two level stacked mold. The mold feeder flow path extends axially from the injector head to a flow distribution block located at the centre of the stacked mold block series. The centrally located distribution block is connected, in sealed relation with the injector head, being axially displaceable therefrom in continuing sealed relation upon the opening of the mold. A drool prevention valve system, located at two of the mold interfaces, to preclude drooling of fluid plastic stock upon opening of the molds includes pressure fluid actuators for operating the valves, wherein the pressure fluid may comprise the fluid plastic stock. The valve system also includes a depressurizing valve provision, wherein, upon opening of the mold interfaces the stock distribution passages are substantially depressurized, to thereby reduce any tendency to drool. The mold includes axial adjustment means to compensate for differential variations in overall mold length within the press, due to changes in effective mold temperature.

This application is a continuation of application Ser. No. 08/908,619,filed Jun. 29, 1992, now abandoned, which is a division of applicationSer. No. 07/544,483 filed Jun. 27, 1990, now U.S. Pat. No. 5,229,145.

TECHNICAL FIELD

This invention is directed to a plastic mold system, and in particular,to a multi-stack mold system

BACKGROUND ART

The use of cavity die molds has progressed from the use of single cavitydies, through multi-cavity dies, to the use of 2-level stacked moldarrangements. In such arrangements, the available axial compressiveforce provided by the molding press is utilized in a pair of moldsarranged in back-to-back relation, so as to effectively double theproductive capacity of the machine for substantially the same pressloading. Such an arrangement gives a doubled production rate with littleincrease in the axial loading required of the press.

The production levels that are presently achievable are limited to2-level stack molding i.e. the number of articles per injection cycle islimited to the total contents of each of two levels, being generallytwice the number of cavities per single mold face or level. One sandwichmolding cycle (Sorensen) has 4-levels of molding cavities. However, theinjection cycle is effectively divided into two sequential cycles,involving re-clamping of the press platen and separate cooling andejection cycles.

The effective working of such arrangements, depends among other things,on the provision of balanced feeder flow paths to all of the diecavities.

The mold stack is subject to differential expansion, axially, betweendifferent groups of parts thereof, namely the hot runner system and themold body.

Various aspects of the prior art relating to injection molding,including die construction for stock flow symmetry; inflow feed nozzles;valve gate actuation; melt or feed transfer, including mold block tomold block stock transfer; drool prevention; mold stack construction;and block heater provisions may be found in the following U.S. patents,cited as being but illustrative of the prior art: 2,770,011 Nov. 1956,Vely; 3,533,594 Oct. 1970, Segmuler; 3,806,295 Apr. 1974, Gellert;3,843,294 Oct. 1974, Bielfeldt et al.; 4,207,051 June 1980, Wright etal.; 4,212,626, July 1980, Gellert; 4,309,163 Jan. 1982, Cottancin;4,473,347 Sept. 1984, Terashima; 4,477,242 Oct. 1984, Eichlseder et al.;4,5389,171 Sep. 1985; 4,586,887 May 1986, Gellert; 4,669,064 July 1986,Landis et al.; 4,663,811 May 1987, Gellert; 4,559,971 June 1987,Gellert.

DISCLOSURE OF THE INVENTION

In accordance with the present invention there is provided a stackedinjection mold system suitable for use with a plurality of four or moremold blocks in mutually stacked relation.

In a mold system embodiment according to the present invention having astacked injection mold containing at least four levels of mold cavitiesin a plurality of mold blocks, stock feed distribution means including afeed block located intermediately of the mold blocks to receive fluentfeed stock from a stock injection head, and stock passage meansconnecting the feed block with the injection head and the mold blocks,in use to transfer stock material simultaneously to the mold cavitiesfrom the injection head; and isolating means to isolate the feed blockfrom feed transfer relation with the mold blocks and the injection head,upon opening of the press.

The separable mold and feed blocks form a plurality of block interfacesbetween each other; stock distribution passage means in the blocks spanthe interfaces thereof when the mold is in a closed condition, the moldblocks being in flow connecting relation with the feed block to formstock flow paths therewith, and drool prevention valves located at theinterfaces to substantially preclude drooling of the plastic stock fromthe flowpaths at the interfaces, upon opening of the interfaces.

The drool prevention valves are preferably located on each side of, andaxially adjoining the respective block interfaces.

In the preferred embodiment the valves are pressure fluid actuated.

In one embodiment the preferred actuating fluid comprises the plasticfluid stock, wherein the valves are actuated, at least in part, inresponse to changes in the pressure of the stock.

In one embodiment stock depressurization valve means are provided inassociation with the stock flow path, being operable in response toforce generating means within the mold, to reduce stock pressure withinthe stock flow path.

The stock depressurization valve force generating means may havepressure responsive actuator means to drive the valve in pressuremodifying relation with the flow path.

The pressure responsive actuator means may include a fluid actuatedpiston having return spring means whereby upon reduction in pressure ofthe fluid acting upon the piston the return spring means becomeeffective to displace the piston, thereby actuating the valve in a localstock depressurizing action.

In an arrangement having a spring driven piston connected in closingrelation with a valve stem, and having a valve head portion movableaxially into sealing relation with a valve seat, the valve seat mayitself be axially movable along the axis of the valve stem, in use topermit axial displacement of the valve head portion and the valve seatin mutual sealing engagement, while effecting a local change in volumeto the stock flow path.

Thus, one embodiment of the invention may comprise a drool preventionvalve for use in a molding apparatus, the valve having a seat portionlocated within a passageway for the passage of fluid therepast, a valvestem connected in controlling relation with a valve head; the head beingdisplaceable axially by the stem into sealing engagement with the seatportion, and guide passage means receiving the seat portion in axiallydisplaceable relation therein, to permit displacement of the head andthe seat in mutually engaged sealing relation along the guide passagemeans, whereby the passageway has the volume thereof effectivelyincreased, in use to diminish the pressure of fluid contained therein.The drool prevention valve may have axial loading means connected withthe valve stem, in displacement controlling relation.

The valve head of the drool prevention valve, located in one of the moldblocks, has an axially outer end face seat; a flow passage abuttmentmeans extending from the adjacent block connecting with the valve endface seat in separable, sealing relation therewith, the abuttment meansbeing movable axially into sealing relation with the valve end face seaton closing of the mold.

The stacked injection mold in accordance with the invention may beprovided with axial adjustment means for compensating for differentialthermal expansion effects related to the effective axial lengths ofcertain of the mold components when in a closed condition,

In the preferred embodiment the axial adjustment means has moveableabuttment means thereof in axial, length compensating relation withstock feed components of the mold; and length-compensating means toadjust the effective axial position of the abuttment means wherebychanges in the forces acting upon the stock feed components due tothermal variations between respective mold components may be effectivelycompensated.

The mold axial adjustment means may include ramp means having aninclined surface movable in wedging relation with an abuttment surfaceof the mold, the angle of inclination of the inclined ramp surface beingless than the angle of friction, in use to preclude overhauling betweenthe inclined surface and the abuttment surface, on the application ofpress closure forces thereagainst during operation of the mold.

In the preferred embodiment ramp positioning means are provided forrepositioning the ramp means relative to the abuttment surface, topermit selective adjustment of closure forces acting against stock flowpath portions of the mold when in a closed condition thereof.

A contamination barrier may be provided about the primary stock flowpath. This flow path extends through that mold block which is positionedin the mold stack at the location closest to the injection head, toconvey heated stock from the injection head, through the mold block tothe distribution block. When the specified mold block is opened, uponthe completion of a molding cycle, for the ejection of the moldedproduct, the provision of a contamination barrier about the stock feederprevents contact of ejected product with the hot outer surface of thestock feeder. In a preferred embodiment the contamination barrier maycomprise a low force coil spring surrounding the exposed axial length ofthe stock feeder, in radially spaced relation therefrom. The coil springbarrier stabilizes thermally at a temperature well below that of thestock flow path, and serves to deflect any molded product fallingagainst the barrier, to preclude contact and sticking of the product tothe feeder, and to prevent accidental contact of an operators hands withthe high temperature surface of the stock feeder.

When the mold stack closes, the coils of the barrier spring compress, tooccupy recesses in the respective block faces, surrounding the stockfeeder.

In operation, upon opening of the mold, the operation of the anti-droolvalves and the axial separation of the mold blocks from the distributionblock serves to isolate the distribution block. However in somecircumstances it may be found that the system can be operated withoutthe occurrence of drooling upon opening of the mold, without theoperation of the anti-drool valves.

BRIEF DESCRIPTION OF THE DRAWINGS

Certain embodiments of the invention are described by way ofillustration, without limitation of the invention thereto, referencebeing made to the accompanying drawings, wherein:

FIG. 1 is a schematic side elevation of a portion of an injectionmolding press having a stacked mold in accordance with the presentinvention mounted therein;

FIG. 2 is a schematic plan view of the stacked mold of FIG. 1;

FIG. 3 is a schematic arrangement showing the stock distribution flowpath of FIGS. 1 and 2;

FIG. 4 is a section taken at 4--4 of FIG. 2, showing one possible molddie arrangement; and,

FIG. 5 is an enlarged detail, in diametrical section, of a portion ofthe FIG. 2 arrangement.

BEST MODE OF CARRYING OUT THE INVENTION

Referring to FIGS. 1 and 2, an injection press 7 for moldingthermoplastic elastomers has an injection head 8 with a movable platen 9and a stationary platen 11, between which is mounted a mold 10, inaccordance with the present invention.

The mold system 10 comprises a 4-layer stacked mold, sized to fit withina standard press, bearing against the mold pressure heads 12 and 14. Astock feeder connection 16 connects with the injector head 8 of press 7.

First and second back-to-back mold blocks 18, 20 are locatedrespectively on opposite sides of a centrally located feed distributorblock 22.

The distributor block 22 is dynamically mobile, in that it is connectedby way of the feeder 32 and feeder connection 16 with the pressinjection head 8, and also with the secondary feeders 38, 40 when in themold-closed condition. Upon opening of the mold the distributor block 22becomes separated from the injection head 8 and also from the moldsecondary feeders 38, 40.

The mold system 10, shown in its closed, operative molding condition,upon completion of the stock injection phase expands axially, byseparation between head 8 and platen 9, on opening of the press.

The head 8 being fixed, the mold head 14 also remains stationary, andmold stack components 20, 18, and 12, together with the feed distributorblock 22 are moved progressively leftwardly, as illustrated, so that therespective four mold interfaces 24, 26, 28 and 30 each opens equally, toan axial extent necessary to permit clear ejection of the moldedcomponents from their respective mold die cavities, while also providingtotal isolation of the feed block.

Synchronized axial displacement of the stacked mold components 12, 18,20 and 22 in relation to the stationary platen 11 and pressure head 14occurs on axially extending arbor bars (not shown), by way ofmechanically synchronized mechanisms, well known in the art (not shown).

Referring to FIGS. 2 and 3, the stock primary feeder 32 is of fixedlength, and is located on the main or polar axis of mold 10.

The primary feeder 32 is secured to the centrally located distributorblock 22, being attached at 16 to the stock feed pressure head 8 whenthe mold is closed, and separating therefrom when the mold 10 is opened.The feeder 32 extends in radially separated relation through mold block20. Upon opening of the mold 10 axial separation of the mold componentstakes place, thereby exposing portions of the stock primary feeder 32outside the associated mold block component parts. At this timeextensible contamination barrier springs 96, detailed below, come intoplay to isolate the feeder 32.

Branch feed connections 34, 36 in distributor block 22 connectrespectively axially forwardly and rearwardly to respective mold feeders38, 40 located in the respective mold blocks 18, 20.

The feeders 38, 40 in turn each branch axially forwardly and rearwardlywithin mold blocks 18, 20 to feed the respective multiple die cavities42 within each of the mold blocks. It will be understood that thequadruple die arrangement of FIG. 4 is purely illustrative, and is notlimiting thereon.

Each double mold 18, 20 has a respective pair of interfaces 28, 30; 24and 26, where the respective molds open, i.e. they "split".

At the mold interfaces 26, 28 there are located anti-drool valvearrangements, comprising a pressure responsive valve 46 located on the"upstream" side of each stock secondary feeder, at the interface; and aremotely actuated valve 48 at the downstream side of interfaces 26, 28.The stock feed paths at the anti-drool valve arrangements open duringthe separation of the mold components

The valve 48 is indicated schematically at interface 26 of FIG. 2, andshown in detail in FIG. 5.

FIG. 5 also shows in more particulars an adjustable mold lock-up loadingsystem 50 having a transversely driven wedge 51, positioned by piston 52in axial loading relation by way of an axial thrust bar 56 actingagainst the end face 54 of the body of valve 48.

In operation the wedge 51 is precisely positioned laterally by a doubleacting hydraulic actuator 58, such that on closure of the press 7 apredetermined closure force is applied to compensate for the effects ofdifferential thermal expansion in the system. The axial force generatedon closure of the press 7, as modified by loading system 50, is appliedat block interfaces 26, 28, to ensure an absence of stock drool or spurtwhen injection pressure is applied. The transverse location of wedge 51,by actuator 48, determines the extent of differential displacement ofthe plastic feeder system flowpaths relative to the mold 10, on closureof the press 7, in order to maintain effective loading at the valveinterfaces 26, 28 to prevent spurt or leakage in the stock secondarydistributors.

Referring to FIG. 5, the branch feed connection 36 terminates in apressure responsive cut off valve 46 at the interface 26. The valve 46is a well known commercial type, of which a number of different makesare normally used for stock flow control at the injector interface.

The radiused seal face 66 of valve 46 connects in stock sealing relationwith seal face 67 of the valve 48, which controls stock flow to the moldfeeder 40.

The valve 48 has a body 68 with stock flow passage 70 therethrough,extending between an upstream seat 72 and lateral port 74, connecting tothe feeder 40.

An elongated valve spindle 76 has a tapered valve head 78, to sealinglyengage the seat 72.

The valve seat 72 is mounted in an axially slidable nose portion 80slidably mounted in a guide passage 81, and secured to valve body 68 topermit displacement in an upstream direction by a distance C, indicatedat 82.

The valve spindle 76 includes a conical piston face 84, and has acontrol piston 86 located within cylinder 88.

A coiled compression spring 90 abuts the downstream end face of controlpiston 86. Pressure fluid connections 92, 94, which may be pneumatic orhydraulic, connect with the respective upstream and downstream ends ofcylinder 88.

Fluid pressure, pneumatic or hydraulic, may be used by way of theconnections 92, 94 to supplement or as a substitute for the spring 90.

In operation, with the press 7 in a closed condition, such thatinterface 26 is tightly closed, the radiused end face 66 of valve 46 isheld in sealing relation with the nose portion 80, forcing the noseportion 80 axially rightwardly, as viewed in the drawings, in adownstream direction to abut its housing, so as to compress the spring90 and take-up the clearance C, at 82.

Upon actuation of the press injector (not shown), to admit fluid stockto the feeder 32, the injection pressure at 36 serves to open the valves46 and 48, admitting the stock by way of the feeder 40 to the respectivemold cavities.

Termination of injection pressure by the press injector reduces stockpressure within the mold 10, so that valves 46 and 48 can both close.

As the press 7 opens, withdrawing end face 66 from nose portion 80, thespring 90 drives the piston 86 leftwardly, to displace valve spindle 76,along with the valve head 78 seated in sealing relation on seat 72,leftwardly in the upstream direction. The nose portion 80 slides axiallyupstream, taking up the clearance C. This displacement increases theinternal flow passage volume adjoining nose portion 80, within moldblock 20, effectively diminishing the internal pressure acting on thefluid feed stock. As the press continues to open, stock flow in the thusdepressurized distributors 18, 20 terminates, and no drooling occurs,either into the mold cavities or between the mold interfaces as the dieseject the molded components.

Closure of the press reverses the travel action of valve 48, andcommencement of a further injection cycle can proceed.

Owing to the generally higher temperature of the injected stock,relative to the mold system, the temperature of the stock feed pathrises, in relation to the mold, which in turn gives rise to differentialthermal expansion of the feed stock distribution means, relative to themold blocks and the feed block.

Referring to the loading adjustment system 50, axial closure forcesapplied by the press 7 are transmitted axially against wedge 51 tothrust members 56, 54, thus determining the axial sealing force andcorresponding reaction force exerted at the respective seal faces 66, 67of the valves 46 and 48. A spring 53 maintains thrust members 56, 54 ina forward, lightly pre-loaded condition.

Prior to closure of the press 7 at start-up the piston 52 of the loadadjustment system 50 may be adjusted radially, in accordance withchanges in the steady state temperature of the mold stack 10 and thefeed stock distribution means. The piston 52 is adjusted radially, so asto allow for the differential axial growth which develops between thestock feed distribution means and the component parts of the mold stack.

Thus, as the temperature of the flow distributor channels initiallyincreases rapidly relative to the mold stack 10, the wedge portion 51 isbacked off, to maintain a substantially constant closure force at thevalve faces 66, 67 of the feed stock distribution means. As thetemperature of mold stack rises, to reach a steady state, the wedge 51may be readjusted, to maintain a consistent range of closure force.

The adjustment provided by the load adjustment system 50 can thus ensurethat sufficient closing force is applied at the respective valveinterfaces to preclude spurting of liquid stock feed, under pressureinto the interspaces of the mold during the production cycles.

The angle A of the wedge portion 51 is selected to be less than theangle of friction of the associated contact faces, so that theapplication of the thermal expansion load, P, cannot produce overhaulingdisplacement forces acting along the wedge 51.

It is contemplated that a load cell may be incorporated in the line ofaction of wedge 51, such as in association with thrust member 56, toprovide an output connected in controlling relation with the actuator58. Such actuation, generally, would be corrective in nature, so thatpositioning of wedge 51 would be corrected at the time of opening of thepress 7, in order to maintain loads applied by the wedge to the thrustmember 56 and associated feed distributor components withinpredetermined safe operational limits for succeeding injection cycles.

Referring to FIGS. 2 and 3, contamination barriers 96 comprisingmulticoil springs 97 contained within recesses 98, 99, serve to protectthe stock feeder 32 against contamination by molded product fallingthereagainst and adhering thereto, when the mold stack is opened. Thesprings 97 also serve an important safety function, to preventaccidental contact by the mold operator with the hot outer surfaces ofprimary feeder 32 which otherwise would be exposed upon opening of thepress 7 and mold 10.

INDUSTRIAL APPLICABILITY

This stacked mold system, is particularly suited to the plastics moldingindustry, for the repetitive mass production of plastic articles byinjection molding.

We claim:
 1. The method of significantly increasing the rate of articleproduction by a stacked mold in a molding press having a predeterminedupper limit to the axial force applied by the press, in holding thestacked components of the mold in closed, mutually compressing relation,including the steps of increasing to at least four levels the number oflevels of mold cavities while maintaining axial symmetry of the levelsabout a central axial position; locating a stock distribution block atthe central axial position; connecting the stock distribution block toan injection head for the press, and to stock flow paths to the moldcavities when the mold is in a closed condition; simultaneouslyinjecting thermoplastic material into all said cavities at substantiallythe same rate of injection; and simultaneously separating and isolatingthe distribution block from the injection head and from the moldcavities during opening of the mold.
 2. The method as set forth in claim1, including the stop of reducing the internal pressure of materialwithin the distribution block during said black separation step, todiminish the likelihood of material spillage.